1. Field of the Invention
The present invention relates, generally, to a communications system with communication terminals connected to a switching system via a packet-oriented communication network and, more particularly, to a communications system wherein a switching system is connected to a communication network via a broadband access unit which has a network access interface, and communication terminals are connected to the communication network via hubs.
2. Description of the Prior Art
Both from German Laid-Open Specification DE 196 04 244 A1, and from Schlichthärle D.: “Hybrid ATM/ISDN Subscriber Connection to a Broadband ISPBX”, Internal Conference on Computer Communication —Proceedings of the Conference—Towards a New World in Computer Communication, 28 Sep. 1992, XP000671919, a communications system is known in which the communication terminals allocated to a switching system are connected to the switching system via an ATM-based communication network. In this arrangement, subscriber interfaces for connecting communication terminals are provided by a number of ATM transfer units—frequently called ATM hubs—which are connected to the ATM-based connection network. The switching system and the ATM hub in each case have an ATM access unit via which, on the one hand, a connection to the ATM-based communication network is implemented and, on the other hand, a bi-directional conversion between the internal data format of the switching system or hub and the data format of the ATM-based communication network is effected.
Modern ATM hubs usually have 64 subscriber interfaces for connecting communication terminals to an ATM-based communication network. In particular, ISDN (Integrated Services Digital Network) communication terminals are connected via S0 interfaces, or digital communication terminals are connected via interfaces derived therefrom such as, for example, UP0 interfaces, via an ATM hub to an ATM-based communication network. In general, a UP0 or an S0 interface includes, on the one hand, two user data channels which, as ISDN-oriented B channels have a transmission rate of in each case 64 kBit/s and, on the other hand, a signalling channel which, as ISDN-oriented D channel, has a transmission rate of 16 kBit/s.
The switching system and the ATM hubs are frequently connected to an ATM-based communication network via a so-called STM1 (Synchronous Transfer Mode) interface having a maximum transmission bit rate of 155 Mbit/s. An access module providing such an STM1 interface is used in communications systems from the company Siemens AG under the internal name “STMA access module”. In the text which follows, this name is used for such access modules having an STM1 interface.
An STMA access module arranged in the switching system currently provides the capability to support 32 subscriber interfaces of an ATM hub connected to an ATM-based communication network; i.e., it is possible to carry out data transmission between the STMA access module and 32 different communication terminals connected to an ATM hub. This only corresponds to a maximum transmission bit rate of 8 Mbit/s via the STM1 interface provided by the STMA access module (having a maximum transmission bit rate of 155 Mbit/s).
Thus, two STMA access modules are necessary in the switching system for supporting all 64 subscriber interfaces of an ATM hub, which is connected via an ATM-based communication network, with the switching system. Since both the STMA access modules and the ATM access unit of an ATM hub only have one STM1 interface in each case, it is necessary to interpose an additional ATM switching module. The ATM switching module concentrates the data to be transmitted between the switching system and the ATM hub from the two STMA access modules onto the ATM access unit of the ATM hub or, respectively, splits these data from the ATM access unit onto the two STMA access modules.
Using an enhanced STMA access module which supports a total of 64 subscriber interfaces there is no need to interpose an additional switching module since an STMA access module expanded in this manner supports all 64 subscriber interfaces of an ATM hub and, thus, these can be connected directly to the enhanced STMA access module. Thus, although only one STM1 interface, provided by an enhanced STMA access module, of the switching system is now occupied for each ATM hub connected to the ATM-based communication network, still only a maximum transmission bit rate of 16 Mbit/s is achieved via the STM1 interface (which has a maximum transmission bit rate of 155 Mbit/s).
It is an object of the present invention, therefore to specify an arrangement by which, when a number of ATM hubs are connected to a packet-oriented communication network, a data transmission can take place between a switching system and the ATM hubs via a network access of the switching system utilizing the transmission bandwidth provided by the network access.